Influenza: Toward understanding the immune response in the young

Development of Influenza-Specific CD4 T Cell-Mediated Immunity in Children Following Inactivated Influenza Vaccination

BACKGROUND

While both cellular and humoral immunity are important in immunologic protection against influenza, how the influenza-specific CD4 T cell response is established in response to early vaccination remains inadequately understood. In this study, we sought to understand how the CD4 T cell response to inactivated influenza vaccine (IIV) is established and develops throughout early childhood.

METHODS

Influenza-specific CD4 T cell responses were quantified following IIV over 2 influenza seasons in 47 vaccinated children between 6 months and 8 years of age who had no documented history of natural influenza infection during the study. Peripheral blood mononuclear cells were stimulated with peptide pools encompassing the translated regions of the pH1, H3, HAB, and NP proteins, and CD4 T cell responses were assessed via multiparameter flow cytometry.

RESULTS

There was boosting of H3- and HAB-specific CD4 T cells but not cells specific for the pH1 HA protein post-vaccination. A positive correlation between age and the magnitude of the influenza-specific CD4 T cell response was seen, with an overall greater magnitude of IFNγ-producing cells in subjects ≥3 years of age. Changes in CD4 T cell functionality were also noted in older compared to younger children, with increases in CD4 T cells producing IFNγ and TNF or IL-2 as well as IFNγ alone.

CONCLUSIONS

Inactivated influenza vaccine elicits a CD4 T cell response to H3 and HAB, with increases in the magnitude of the CD4 T cell response and changes in cellular functionality throughout childhood. This suggests that repeated influenza vaccination contributes to the development of anti-influenza CD4 T cell memory in children.

Hemagglutination Inhibition Antibody Titers as Mediators of Influenza Vaccine Efficacy Against Symptomatic Influenza A(H1N1), A(H3N2), and B/Victoria Virus Infections

BACKGROUND

The hemagglutination inhibition antibody (HAI) titer contributes only a part of vaccine-induced protection against influenza virus infections. Using causal mediation analysis, we quantified the proportion of vaccine efficacy mediated by postvaccination HAI titers.

METHODS

We conducted causal mediation analyses using data from a randomized, active-comparator controlled, phase III, trial of an inactivated, split-virion seasonal quadrivalent influenza vaccine in children conducted from October 2010 to December 2011 in 8 countries. Vaccine efficacy was estimated using a weighted Cox proportional hazards model. Estimates were decomposed into the direct and indirect effects mediated by postvaccination HAI titers.

RESULTS

The proportions of vaccine efficacy mediated by postvaccination HAI titers were estimated to be 22% (95% confidence interval, 18%--47%) for influenza A(H1N1), 20% (16%-39%) for influenza A(H3N2), and 37% (26%-85%) for influenza B/Victoria.

CONCLUSIONS

HAI titers partially mediate influenza vaccine efficacy against influenza A(H1N1), A(H3N2), and B/Victoria. Our estimates were lower than in previous studies, possibly reflecting expected heterogeneity in antigenic similarity between vaccine and circulating viruses across seasons.

Human Infant Fecal Microbiota Differentially Influences the Mucosal Immune Pathways Upon Influenza Infection in a Humanized Gnotobiotic Pig Model

In this study, we evaluated the impact of human gut microbiota on the immune pathways in the respiratory tract using a gnotobiotic (Gn) piglet model. We humanized piglets with rural and urban infant fecal microbiota (RIFM and UIFM, respectively) and then infected them with a H1N1 swine influenza virus. We analyzed the microbial diversity and structure of the intestinal and respiratory tracts of the piglets before and after the influenza virus infection and measured the viral load and immune responses. We found that the viral load in the upper respiratory tract of UIFM transplanted piglets was higher than their rural cohorts (RIFM), while virus-specific antibody responses were comparable. The relative cytokine gene expression in the tracheobronchial (respiratory tract) and mesenteric (gastrointestinal) lymph nodes, lungs, blood, and spleen of RIFM and UIFM piglets revealed a trend in reciprocal regulation of proinflammatory, innate, and adaptive immune-associated cytokines as well as the frequency of T-helper/memory cells, cytotoxic T cells, and myeloid immune cell subsets. We also observed different phylum-level shifts of the fecal microbiota in response to influenza virus infection between the two piglet groups, suggesting the potential impact of the gut microbiota on the immune responses to influenza virus infection and lung microbiota. In conclusion, Gn piglets humanized with diverse infant fecal microbiota had differential immune regulation, with UIFM favoring the activation of proinflammatory immune mediators following an influenza virus infection compared to their rural RIFM cohorts. Furthermore, Gn piglets can be a useful model in investigating the impact of diverse human microbiota of the gastrointestinal tract, probably also the respiratory tract, on respiratory health and testing specific probiotic- or prebiotic-based therapeutics.

Risk factors for pneumonia among children with coinfection of influenza A virus and Mycoplasma pneumoniae

OBJECTIVE

To investigate the clinical characteristics and risk factors for pneumonia in children co-infected with influenza A virus (IAV) and Mycoplasma pneumoniae (MP).

METHODS

Children who were diagnosed with IAV and MP infection between January and December, 2023 were enrolled and divided into a non-pneumonia group and a pneumonia group. Univariate analysis and logistic regression analysis were used to evaluate each index, and the risk factors for pneumonia caused by coinfection in the two groups were explored.

RESULTS

A total of 209 patients were enrolled, of which 107 and 102 patients were in the pneumonia and non-pneumonia groups, respectively. The patients in the pneumonia group were older and had a longer duration of fever (P < 0.05). Univariate analysis revealed that the median age, duration of fever, and CD3+, CD4+, CD8+ and IL-10 levels were significantly correlated with pneumonia (P < 0.05). Multivariate logistic regression analysis revealed that the median age, duration of fever, and CD4+, CD8+ and IL-10 levels were independent risk factors for pneumonia. Area under the curve of the five combined indicators in the ROC (receiver operator characteristic) analysis was 0.883, was higher than single factor.

CONCLUSION

Children with IAV and MP infection whose age older than 6.08 years, had a fever longer than 4 days, had a CD4+ count < 22.12%, had a CD8+ count < 35.21%, had an IL-10 concentration > 22.08 ng/ml were more likely to develop pneumonia.

Vaccine Effectiveness Against Pediatric Influenza-A-Associated Urgent Care, Emergency Department, and Hospital Encounters During the 2022-2023 Season: VISION Network

BACKGROUND

During the 2022-2023 influenza season, the United States experienced the highest influenza-associated pediatric hospitalization rate since 2010-2011. Influenza A/H3N2 infections were predominant.

METHODS

We analyzed acute respiratory illness (ARI)-associated emergency department or urgent care (ED/UC) encounters or hospitalizations at 3 health systems among children and adolescents aged 6 months-17 years who had influenza molecular testing during October 2022-March 2023. We estimated influenza A vaccine effectiveness (VE) using a test-negative approach. The odds of vaccination among influenza-A-positive cases and influenza-negative controls were compared after adjusting for confounders and applying inverse-propensity-to-be-vaccinated weights. We developed overall and age-stratified VE models.

RESULTS

Overall, 13 547 of 44 787 (30.2%) eligible ED/UC encounters and 263 of 1862 (14.1%) hospitalizations were influenza-A-positive cases. Among ED/UC patients, 15.2% of influenza-positive versus 27.1% of influenza-negative patients were vaccinated; VE was 48% (95% confidence interval [CI], 44-52%) overall, 53% (95% CI, 47-58%) among children aged 6 months-4 years, and 38% (95% CI, 30-45%) among those aged 9-17 years. Among hospitalizations, 17.5% of influenza-positive versus 33.4% of influenza-negative patients were vaccinated; VE was 40% (95% CI, 6-61%) overall, 56% (95% CI, 23-75%) among children ages 6 months-4 years, and 46% (95% CI, 2-70%) among those 5-17 years.

CONCLUSIONS

During the 2022-2023 influenza season, vaccination reduced the risk of influenza-associated ED/UC encounters and hospitalizations by almost half (overall VE, 40-48%). Influenza vaccination is a critical tool to prevent moderate-to-severe influenza illness in children and adolescents.

The role of viral interference in shaping RSV epidemics following the 2009 H1N1 influenza pandemic

Respiratory syncytial virus (RSV) primarily affects infants, young children, and older adults, with seasonal outbreaks in the United States (US) peaking around December or January. Despite the limited implementation of non-pharmaceutical interventions, disrupted RSV activity was observed in different countries following the 2009 influenza pandemic, suggesting possible viral interference from influenza. Although interactions between the influenza A/H1N1 pandemic virus and RSV have been demonstrated at an individual level, it remains unclear whether the disruption of RSV activity at the population level can be attributed to viral interference. In this work, we first evaluated changes in the timing and intensity of RSV activity across 10 regions of the US in the years following the 2009 influenza pandemic using dynamic time warping. We observed a reduction in RSV activity following the pandemic, which was associated with intensity of influenza activity in the region. We then developed an age-stratified, two-pathogen model to examine various hypotheses regarding viral interference mechanisms. Based on our model estimates, we identified three mechanisms through which influenza infections could interfere with RSV: 1) reducing susceptibility to RSV coinfection; 2) shortening the RSV infectious period in coinfected individuals; and 3) reducing RSV infectivity in coinfection. Our study offers statistical support for the occurrence of atypical RSV seasons following the 2009 influenza pandemic. Our work also offers new insights into the mechanisms of viral interference that contribute to disruptions in RSV epidemics and provides a model-fitting framework that enables the analysis of new surveillance data for studying viral interference at the population level.

Risk factors for death associated with severe influenza in children and the impact of the COVID-19 pandemic on clinical characteristics

Background

To summarize the clinical features of severe influenza in children and the high-risk factors for influenza-related deaths and to raise awareness among pediatricians.

Methods

A retrospective study of clinical manifestations, laboratory tests, and diagnosis and treatment of 243 children with severe influenza admitted to Shenzhen Children's Hospital from January 2009 to December 2022 was conducted. Univariate logistic regression analysis and Boruta analysis were also performed to identify potentially critical clinical characteristics associated with death, and clinically significant were used in further multivariate logistic regression analysis. Subject receiver operating characteristic (ROC) curves were applied to assess the efficacy of death-related independent risk factors to predict death from severe influenza.

Results

There were 169 male and 74 female patients with severe influenza, with a median age of 3 years and 2 months and 77.4% of patients under six. There were 46 cases (18.9%) in the death group. The most common pathogen was Influenza A virus (IAV) (81.5%). The most common complication in the death group was influenza-associated acute necrotizing encephalopathy (ANE [52.2%]). Severe influenza in children decreased significantly during the COVID-19 pandemic, with a median age of 5 years, a high predominance of neurological symptoms such as ANE (P = 0.001), and the most common pathogen being H3N2 (P < 0.001). D-dimer, acute respiratory distress syndrome (ARDS), and acute necrotizing encephalopathy (ANE) were significant independent risk factors for severe influenza-associated death. Furthermore, the ROC curves showed that the combined diagnosis of independent risk factors had significant early diagnostic value for severe influenza-related deaths.

Conclusion

Neurological disorders such as ANE are more significant in children with severe influenza after the COVID-19 pandemic. Influenza virus infection can cause serious multisystem complications such as ARDS and ANE, and D-dimer has predictive value for early diagnosis and determination of the prognosis of children with severe influenza.

Influenza Vaccination Coverage Rates and Determinants in Greek Children until the Age of Ten (2008-2019), the Rhea Mother-Child Cohort

BACKGROUND

In Greece, influenza vaccination is currently recommended for children with high-risk conditions. There are limited data on influenza vaccination uptake among Greek children with and without high-risk conditions. We aim to describe the annual influenza vaccination uptake until the age of ten in a population-based mother-child cohort and identify the factors influencing vaccination rates.

METHODS

Immunization data from the child's health cards at 4 and 10 years were available for 830 and 298 children participating in the Rhea cohort (2008-2019). We calculated vaccination coverage by age, winter season and among children with asthma and obesity for whom the vaccine is indicated. Univariable and multivariable stepwise logistic regression models were utilized to identify the association between several sociodemographic, lifestyle and health-related variables and vaccine uptake by age four.

RESULTS

By the ages of four and ten, 37% and 40% of the children, respectively, had received at least one influenza vaccination. Only 2% of the children were vaccinated for all winter seasons during their first four years of life. The vaccination rate was highest at the age of two and during the 2009-2010 season. Vaccination rates for children with asthma and obesity were 18.2% and 13.3% at age four and 8.3% and 2.9% at age ten. About 10% of all vaccines were administered after December and 24% of the children received only one dose upon initial vaccination. Children with younger siblings and those who had experienced more respiratory infections were more likely to be vaccinated by the age of four, while children exposed to smoking were less likely to be vaccinated.

CONCLUSIONS

Children in our study were more likely to be vaccinated against influenza at an early age with the peak occurring at the age of two. Nonetheless, annual vaccination uptake was uncommon. Vaccination rates of children with asthma and obesity were well below the national target of 75% for individuals with chronic conditions. Certain groups may merit increased attention in future vaccination campaigns such as children raised in families with unfavourable health behaviours.

Albicanol antagonizes PFF-induced mitochondrial damage and reduces inflammatory factors by regulating innate immunity

As an environmental pollutant, profenofos (PFF) can seriously endanger human health through the food chain. Albicanol is a sesquiterpene compound with antioxidant, anti-inflammatory, and anti-aging properties. Previous studies have shown that Albicanol can antagonize apoptosis and genotoxicity caused by PFF exposure. However, the toxicity mechanism of PFF regulating hepatocyte immune function, apoptosis, and programmed necrosis and the role of Albicanol in this process have not been reported yet. In this study, grass carp hepatocytes (L8824) were treated with PFF (200 μM) or combined with Albicanol (5 ×10^-5 μg mL^-1) for 24 h to establish an experimental model. The results of JC-1 probe staining and Fluo-3 AM probe staining showed increased free calcium ions and decreased mitochondrial membrane potential in L8824 cells after PFF exposure, suggesting that PFF exposure may lead to mitochondrial damage. Real-time quantitative PCR and Western blot results showed that PFF exposure could increase the transcription of innate immunity-related factors (C3, Pardaxin 1, Hepcidin, INF-γ, IL-8, and IL-1β) in L8824 cells. PFF up-regulated the TNF/NF-κB signaling pathway and the expression of caspase-3, caspase-9, Bax, MLKL, RIPK1, and RIPK3 and down-regulated the expression of Caspase-8 and Bcl-2. Albicanol can antagonize the above-mentioned effects caused by PFF exposure. In conclusion, Albicanol antagonized the mitochondrial damage, apoptosis, and necroptosis of grass carp hepatocytes caused by PFF exposure by inhibiting the TNF/NF-κB pathway in innate immunity.

Multi-omics association analysis reveals interactions between the oropharyngeal microbiome and the metabolome in pediatric patients with influenza A virus pneumonia

Children are at high risk for influenza A virus (IAV) infections, which can develop into severe illnesses. However, little is known about interactions between the microbiome and respiratory tract metabolites and their impact on the development of IAV pneumonia in children. Using a combination of liquid chromatography tandem mass spectrometry (LC-MS/MS) and 16S rRNA gene sequencing, we analyzed the composition and metabolic profile of the oropharyngeal microbiota in 49 pediatric patients with IAV pneumonia and 42 age-matched healthy children. The results indicate that compared to healthy children, children with IAV pneumonia exhibited significant changes in the oropharyngeal macrobiotic structure (p = 0.001), and significantly lower microbial abundance and diversity (p < 0.05). These changes came with significant disturbances in the levels of oropharyngeal metabolites. Intergroup differences were observed in 204 metabolites mapped to 36 metabolic pathways. Significantly higher levels of sphingolipid (sphinganine and phytosphingosine) and propanoate (propionic acid and succinic acid) metabolism were observed in patients with IAV pneumonia than in healthy controls. Using Spearman’s rank-correlation analysis, correlations between IAV pneumonia-associated discriminatory microbial genera and metabolites were evaluated. The results indicate significant correlations and consistency in variation trends between Streptococcus and three sphingolipid metabolites (phytosphingosine, sphinganine, and sphingosine). Besides these three sphingolipid metabolites, the sphinganine-to-sphingosine ratio and the joint analysis of the three metabolites indicated remarkable diagnostic efficacy in children with IAV pneumonia. This study confirmed significant changes in the characteristics and metabolic profile of the oropharyngeal microbiome in pediatric patients with IAV pneumonia, with high synergy between the two factors. Oropharyngeal sphingolipid metabolites may serve as potential diagnostic biomarkers of IAV pneumonia in children.